This invention relates to casting of molten metal into ingot form and, more particularly, to static vacuum casting of ingots.
Vacuum refining and casting of ingots, as described, for example, in U.S. Pat. No. 4,838,340 to Entrekin et al. and U.S. Pat. Nos. 4,932,635 and 4,936,375 to Harker, has been completed by pouring molten metal into a vertically disposed water-cooled mold in which an ingot is formed and solidified and drawn downwardly as molten metal is added to the top of the mold. Because of the relative motion between the metal being solidified and the adjacent cold surface of the mold, laps and cold shuts tend to be formed, producing an ingot with a rough surface which must be ground or otherwise treated if a smooth-surfaced ingot is desired. Moreover, the cross-sectional shape of the ingot must be uniform throughout its length since it is determined by the cross-sectional configuration of the mold.
The patent to DeWeese et al., U.S. Pat. No. 3,581,809, discloses a continuous casting device in the shape of a continuously rotating drum having water-cooled molds at its peripheral surface into which molten metal is poured as the drum is rotated. Such continuous casting into separate mold elements followed by rapid cooling and solidification leads to shrinkage porosity within and at the surface of the molded ingots and may result in solidified metal bridges which physically connect adjacent ingots and makes it difficult to separate the ingots from the mold.
Furthermore, such casting arrangements rely on high metal casting rates to maintain a steady stream of metal into a mold and minimize the time for heat loss from the source to the mold. However, if the melting, refining and casting processes are in line, this can require flow rates above the desired or possible melting and refining capabilities of the system. Moreover, a high casting rate requires a correspondingly high solidification rate, resulting in porous castings.